Photoelectric conversion apparatus and imaging system using the same

ABSTRACT

In a photoelectric conversion apparatus including charge storing portions in its imaging region, isolation regions for the charge storing portions include first isolation portion each having a PN junction, and second isolation portions each having an insulator. A second isolation portion is arranged between a charge storing portion and at least a part of a plurality of transistors.

TECHNICAL FIELD

The present invention relates to an element isolation configuration in aphotoelectric conversion apparatus including charge storing portions.

BACKGROUND ART

In recent years, many digital cameras and digital camcorders have usedCCD-type or MOS-type photoelectric conversion apparatuses. For MOS-typephotoelectric conversion apparatuses, element structures for deliveringglobal shuttering that provides uniform accumulation time forphotoelectric conversion portions have been developed. Such structuresare components each including a charge storing portion for aphotoelectric conversion portion. Japanese Patent Application Laid-OpenNo. 2007-053217 discloses a configuration in which components eachincluding a charge storing portion each include an isolation region witha LOCOS structure. Also, Japanese Patent Application Laid-Open No.2007-157912 discloses a configuration in which a gap are provided so asto surround each charge storing portion for reducing the amount of lightincident on the charge storing portion in the component including thecharge storing portion.

DISCLOSURE OF THE INVENTION

A photoelectric conversion apparatus according to an aspect of thepresent invention comprises a pixel unit including: a photoelectricconversion portion including at least a first photoelectric conversionelement; a charge storing portion including at least a first chargestorage element, and holding a charge generated in the photoelectricconversion portion; a plurality of transistors for outputting a signalbased on the charge held by the charge storing portion; and an isolationarea for electrically isolating the charge storing portion, wherein theisolation area includes a first isolation portion having a PN junction;and a second isolation portion having an insulator and arranged betweenthe first charge storage element and at least a part of the plurality oftransistors.

Also, am image pickup system according to another aspect of the presentinvention includes: the foregoing imaging apparatus, an optical systemfor forming an image on an imaging plane in the imaging apparatus; and asignal processing unit for processing signals output from the imagingapparatus to generate image data.

Other features and advantages of the present invention will be apparentfrom the following description taken in conjunction with theaccompanying drawings, in which like reference characters designate thesame or similar parts throughout the figures thereof.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates an example of a pixel circuit in a photoelectricconversion apparatus.

FIG. 2 is a schematic plan view of a photoelectric conversion apparatusfor describing a first exemplary embodiment.

FIG. 3A is a schematic cross-sectional view taken along line 3A-3A inFIG. 2.

FIG. 3B is a schematic cross-sectional view taken along line 3B-3B inFIG. 2.

FIG. 4 is a schematic plan view of a photoelectric conversion apparatusfor describing a second exemplary embodiment.

FIG. 5A is a schematic cross-sectional view taken along line 5A-5A inFIG. 4.

FIG. 5B is a schematic cross-sectional view taken along line 5B-5B inFIG. 4.

FIG. 6A is a schematic plan view of a photoelectric conversion apparatusfor describing a first exemplary embodiment.

FIG. 6B is a schematic cross-sectional view of a photoelectricconversion apparatus for describing a first exemplary embodiment.

FIG. 7 illustrates another example of a pixel circuit in a photoelectricconversion apparatus.

FIG. 8 is a block diagram for describing an imaging system.

The accompanying drawings, which are incorporated in and constitute apart of the specification, illustrate embodiments of the invention and,together with the description, serve to explain the principles of theinvention.

BEST MODES FOR CARRYING OUT THE INVENTION

The present inventors have discovered that when light enters anisolation region in the structure disclosed in Japanese PatentApplication Laid-Open No. 2007-053217, diffuse reflection of lightoccurs in the isolation region, resulting in the light entering thecharge storing portion. Japanese Patent Application Laid-Open No.2007-157912 discusses entrance of light around a wiring layer, but doesnot discuss the effect imposed on the charge storing portion when lightenters the isolation region. However, for the isolation regions, it isnecessary to consider not only the effect of light, but also electriccharacteristics such as pressure resistance and parasitic MOS.Therefore, an object of the present invention is to provide aphotoelectric conversion apparatus that reduces intrusion of chargesfrom isolation regions into charge storing portions.

The present invention relates to a photoelectric conversion apparatusincluding charge storing portions in its imaging region. In suchphotoelectric conversion apparatus, an isolation region for a chargestoring portion includes a first isolation portion having a PN junction,and a second isolation portion having an insulator. The second isolationportion is arranged between the charge storing portion and a least apart of a plurality of transistors. The first isolation portion reducesthe effect of diffuse reflection occurring in the isolation regionhaving an oxide film, and arrangement of the second isolation portionbetween the charge storing portion and the transistors enablesmaintenance of pressure resistance of a readout circuit and the chargestoring portion.

Hereinafter, exemplary embodiments will be described with reference tothe drawings. The description will be provided considering signalcharges as electrons.

First Exemplary Embodiment

First, an example of a pixel circuit in a photoelectric conversionapparatus including charge storing portions will be described withreference to FIG. 1. FIG. 1 illustrates a configuration in which pixels13 each including a charge storing portion are arranged in two rows andtwo columns. Each pixel 13 includes a photoelectric conversion portion2, a charge storing portion 3, a floating diffusion region 4, a powersource portion 5, a pixel output portion 7, a first transfer gateelectrode 8, a second gate electrode 9, a gate electrode 10 of a resettransistor, a gate electrode 11 of a selection transistor, a gateelectrode 12 of an amplification transistor, and a gate electrode 23 ofan overflow drain (hereinafter, “OFD”), which serves as a dischargingportion. A power source line, which is a wiring for supply apredetermined voltage, is connected to the power source portion 5. Here,the power source portion 5 shares the same node with the drain of thereset transistor, the drain of the selection transistor and the drain ofthe OFD. Control lines RES, TX1, TX2, SEL and OFD supply pulses to therespective gate electrodes. The control line RES supplies pulses to thegate electrode 10 of the reset transistor, the control line TX1 suppliespulses to the first gate electrode 8, the control line TX2 suppliespulses to the second gate electrode 9, the control line SEL suppliespulses to the gate electrode 11 of the selection transistor, and thecontrol line OFD supplies pulses to the gate electrode 23 of theoverflow drain. A signal line OUT is also provided. The numbers n and mare positive integers: rows n and their respective adjacent rows n+1,and a column m and its adjacent column m+1 are illustrated. Here, apixel 13, which is a component including one photoelectric conversionportion 2, is a minimum unit of repetition in the configuration of thephotoelectric conversion apparatus. A region in which a plurality of thepixels 13 is arranged is referred to as an imaging region.

A global shutter in the pixels 13 described above operates as follows.After a lapse of certain accumulation time, charges generated in thephotoelectric conversion portions 2 are transferred to the chargestoring portions 3 by means of the first gate electrodes 8. During thesignal charges for the certain accumulation time being held in thecharge storing portions 3, the photoelectric conversion portions 2 startsignal charge accumulation again. The signal charges in the chargestoring portions 3 are transferred to the floating diffusion regions 4by means of the second gate electrodes 9, and output from the pixeloutput portions 7 of the amplification transistors as signals. Also, inorder to prevent the charges generated in the photoelectric conversionportions 2 during the signal charges being held in the charge storingportions 3 from intruding into the charge storing portions 3, thecharges in the photoelectric conversion portions 2 may be discharged viathe OFDs 23. Each reset transistor sets its floating diffusion region 4to have a predetermined potential before the transfer of the signalcharges from the charge storing portions 3 (reset operation). Thepotentials of the floating diffusion regions 4 at this point of time areoutput from the pixel output portions 7 as noise signals todifferentiate the noise signals from signals based on signal chargesthat are output later, enabling removal of the noise signals.

Also, each pixel 13 may have a buried channel below its first gateelectrode 8. In other words, the photoelectric conversion portions 2 andthe charge storing portions 3 are electrically connected. A globalshutter having such configuration operates as follows. Signal chargesgenerated in the photoelectric conversion portions 2 are held in thephotoelectric conversion portions 2 and the charge storing portions 3.After a lapse of certain accumulation time, the signal charges aretransferred to the floating diffusion regions 4 by means of the secondgate electrodes 9. After the transfer of the signal charges to thefloating diffusion regions 4, the photoelectric conversion portions 2and the charge storing portions 3 start signal charge accumulationagain. In this configuration, also, in order to prevent the chargesgenerated in the photoelectric conversion portions 2 during the signalcharges being held in the floating diffusion regions 4 from intrudinginto the floating diffusion regions 4, the charges in the photoelectricconversion portions 2 may be discharged via the OFDs 23. Also, theoperation of the reset transistors is similar to that in the foregoingcase. This operation can be performed by means of driving the first gateelectrodes 8 even though no buried channels are provided below the firstgate electrodes 8. The present exemplary embodiment will be describedtaking such configuration provided with buried channels as an example.

FIG. 2 is a schematic plan view of a photoelectric conversion apparatuswith the pixel configuration illustrated in FIG. 1. The pixels 13 arearranged in two rows and two columns. The pixels 13 include a firstpixel 13 a, a second pixel 13 b, a third pixel 13 c and a fourth pixel13 d. Components having similar functions as those in FIG. 1 areprovided with the same reference numerals and a description thereof willbe omitted. Letters “a”, “b”, “c” and “d” in the reference numeralsindicate that the relevant components are of the first pixel, the secondpixel, the third pixel and the fourth pixel, respectively. Furthermore,for ease of description, arrangement of contacts and wirings other thanthe gate electrodes is not illustrated. The parts sharing the same nodein FIG. 1 may be included in the same semiconductor region or may beconnected via wirings.

FIG. 1 illustrates isolation regions 1 and 14. Each isolation region 14is a first isolation portion having a PN junction in a semiconductorregion, and each isolation region 1 is a second isolation portion havingan insulator. The part other than the second isolation portion 1 is anactive region where elements are formed.

A description will be provided focusing on the first pixel 13 a. Thefirst gate electrode 8 a extends to an area above the charge storingportion 3 a. As a result of the first gate electrode 8 a extending to anarea above the charge storing portion 3 a, the amount of light incidenton the charge storing portion 3 a can be reduced, and the amount of darkcurrent in the charge storing portion 3 a can be reduced by controllinga voltage supplied to the first gate electrode 8 a. Here, the chargestoring portion 3 a includes a first isolation portion 14 and a secondisolation portion 1. The first isolation portion 14 is arranged betweenthe charge storing portion 3 a and an adjacent photoelectric conversionportion 2 (not illustrated). In other words, for example, a firstisolation portion 14 is arranged between a charge storing portion 3 b ofthe second pixel 13 c and the charge storing portion 3 a of the firstpixel 13 a. The configuration of such isolation regions will bedescribed in details with reference to the schematic cross-sectionalviews in FIGS. 3A and 3B. Hereinafter, a description will be providedreferring “n-type” as “first conductivity type”.

FIG. 3A is a schematic cross-sectional view taken along line 3A-3A inFIG. 2, and FIG. 3B is a schematic cross-sectional view taken along line3B-3B in FIG. 2. FIGS. 3A and 3B each illustrate a well 21. The well 21may be either of n-type or p-type, and may also be a component providedon a semiconductor substrate or a semiconductor substrate. A secondconductivity type first semiconductor region 16 and a first conductivitytype second semiconductor region 17 constitute a photoelectricconversion portion 2. A first conductivity type third semiconductorregion 18 constitutes a charge storing portion 3. A second conductivitytype fourth semiconductor region 19 can function as a barrier forreducing the intrusion of electrons into the charge storing portion 3. Alight shielding film 20 reduces the amount of light incident on thecharge storing portion 3. In FIG. 2, the light shielding films 20 areomitted. A second conductivity type semiconductor region 22 constitutesa first isolation portion 14 for providing electrical isolation from thesurrounding semiconductor regions, using PN junctions. The secondconductivity type semiconductor region 14 has a higher concentration ofsecond conductivity type impurities compared to those of the surroundingsemiconductor regions, that is, has a high potential for signalcarriers. Also, an insulator 23 constitutes a second isolation portion1. The second isolation portion 1 is formed in a LOCOS (local oxidationof silicon) structure or an STI (shallow trench isolation) structure. Asecond conductivity type fifth semiconductor region 15 can function as achannel stop or a barrier for electrons. Furthermore, the fifthsemiconductor region 15 may have a function that prevents dark currentgenerated as a result of providing the insulator 23. Here, in thepresent exemplary embodiment, a first conductivity type sixthsemiconductor region (not illustrated) is provided between the secondsemiconductor region 17 and the third semiconductor region 18. A buriedchannel is formed below the first gate electrode 8 by the sixthsemiconductor region.

Here, a detailed description will be provided in relation to the objectof the present invention with reference to FIGS. 6A and 6B. FIG. 6A is aschematic plan view corresponding to FIG. 2, and as with FIG. 2,corresponds to the pixel circuit in FIG. 1. FIG. 6B is a schematiccross-sectional view taken along line X-Y in FIG. 6A. The componentssimilar to those in FIGS. 1 to 3B are provided with the same referencenumerals, and a description thereof will be omitted. Here, in FIG. 6A,only the second isolation portions 1 each having an insulator areprovided as isolation regions for the charge storing portions 3. In thecross-section along line X-Y in this case, a phenomenon as illustratedin FIG. 6B occurs. Since the photoelectric conversion portion 2 aincludes no light shielding film 20, light easily enters thephotoelectric conversion portion 2 a, resulting in light also entersbetween the photoelectric conversion portion 2 a and the charge storingportion 3 b. Here, the present inventors have discovered that when lightenters a second isolation portion 1, reflection is repeated on theinterface between the insulator and the semiconductor substrate 21,resulting in generation of scattered light running in variationdirections. Electrons generated by this scattered light may intrude intosignal charge held in the charge storing portion 3 b, causing alias(error signal). In this case, if the isolation region is formed by anSTI structure in which the insulator extends to a deep portion of thesemiconductor substrate, reflection occurs more easily and thus,scattered light is easily generated. Also, light may enter the isolationregion not only via the periphery of the photoelectric conversionportion 2 a, but also via a cut of the light shielding film 20 even whenthe charge storing portion 3 b is provided adjacent to the isolationregion.

Meanwhile, in FIG. 3A, a first isolation portion 14 is provided betweenthe charge storing portion 3 b of the second pixel 13 b and thephotoelectric conversion portion 2 a of the first pixel 13 a. Asillustrated in FIG. 3A, light easily enters the photoelectric conversionportion 2 a provided with no light shielding film 20. As a result ofproviding the first isolation portion 14 in this part with a largeamount of incident light, the light penetrates to a deep part of thewell 21, reducing scattering. Also, the first isolation portion 14enables reduction of intrusion of electrons generated by light into thethird semiconductor region 18 b constituting the charge storing portion3 b. Furthermore, the existence of a fourth semiconductor region 19 benables further reduction of intrusion of electrons into the thirdsemiconductor region 18 b.

Also, in FIG. 3B, a second isolation portion 1 is arranged between atleast a part of a plurality of transistors (here, a reset transistor)and the charge storing portion 3 a. Sufficient electric isolation can beprovided by the second isolation portion 1. It should be noted that thetransistor is not limited to the reset transistor: it is only necessarythat the charge storing portion should not share the same node with thesource or drain region of the transistor; and the transistor may be anamplification transistor or a selection transistor. Electric isolationand pressure resistance are needed because high pulses may be suppliedto these transistor gate electrodes, and a high voltage may be thesource or drain regions of the transistors. Furthermore, a secondisolation portion may be arranged between a charge storing portion and asemiconductor region well for a well contact for fixing the potential.This is intended to provide sufficient electric isolation of the chargestoring portion from the semiconductor region for the well contactbecause during reset operation, a high potential is applied to thecharge storing portion.

Here, in many cases, a semiconductor region constituting the source ordrain region of a transistor has a higher impurity concentrationcompared to that of a second semiconductor region 17 constituting aphotoelectric conversion portion. If isolation of such semiconductorregion having a high impurity concentration is provided by a firstisolation portion, a large electric field will be applied to the PNjunction interface. Accordingly, it is desirable to provide electricisolation while the pressure resistance being kept, by means of a secondisolation portion 1. Furthermore, the plurality of transistors can blocklight, which is different from the photoelectric conversion portion 2,and thus, the amount of light incident on the second isolation portion 1can be reduced, enabling reduction of generation of scattered light.However, a second isolation portion 1 having an insulator may cause darkcurrent, which arises from a defect in the lattice on the interfacebetween the insulator and the semiconductor. Therefore, as in thepresent exemplary embodiment, a first isolation portion 14 is arrangednear a charge storing portion 3 or a photoelectric conversion portion 2,which holds signal charges, enabling reduction of noise compared to theconfiguration illustrated in FIG. 6.

The above-described configuration enables provision of an imagingapparatus that reduces intrusion of charges from isolation regions intocharge storing portions while having pressure resistance.

In a configuration in which a buried channel is provided between aphotoelectric conversion portion 2 and a charge storing portion 3 as inthe present exemplary embodiment, the time during which signal chargesare held in the charge storing portion 3 become long, and thus, theconfiguration is effective for reduction of intrusion of electronsgenerated by incident light as well as reduction of dark current.However, the configuration in the present invention is not limited toone in which a buried channel is provided between a photoelectricconversion portion 2 and a charge storing portion 3. Furthermore, thefourth semiconductor region 19 and the fifth semiconductor region 15,which serve as barriers, may not be provided.

Second Exemplary Embodiment

A photoelectric conversion apparatus according to the present exemplaryembodiment is different from that of the first exemplary embodiment in aplan layout of pixels, and has a configuration in which pixels arearranged symmetrically with reference to lines. Also, the photoelectricconversion apparatus is different from the first exemplary embodiment inarrangement of the isolation regions around the charge storing portionsand photoelectric conversion portion. A description will be providedwith reference to FIG. 4.

FIG. 4 is a schematic plan view of a photoelectric conversion apparatus.In FIG. 4, the same components as those in FIG. 2 are provided with thesame reference numerals, and a description thereof will be omitted. Forease of description, contacts, wirings other than gate electrodes, andlight shielding films are not illustrated. Although FIG. 4 illustrateseight pixels 13, which are arranged in two rows and four columns, theeight pixels in FIG. 4 are repeatedly arranged in two dimensions for theentire photoelectric conversion apparatus. A description will beprovided using four pixels 13 a, 13 b, 13 c and 13 d from among thepixels. In FIG. 4, photoelectric conversion portions 2 of the firstpixel 13 a and the third pixel 13 c arranged facing each other, which isdifferent from FIG. 2. In other words, the column of the first pixel 13a and the second pixel 13 b and the column of the third pixel 13 c andthe fourth pixel 13 d are arranged symmetrically with reference to aline. Here, as in the first exemplary embodiment, a first isolationportion 14 is arranged between a charge storing portion 3 a of the firstpixel 13 a and a photoelectric conversion portion of an adjacent pixel(not illustrated). A second isolation portion 1 is arranged between atransistor in the first pixel 13 a and the charge storing portion 3 a.However, the first isolation portion 14 is also arranged between thecharge storing portion 3 a of the first pixel 13 a and a charge storingportion 3 c of the third pixel 13 c. Such configuration enables furtherreduction of charges intruding into the charge storing portion 3 acompared to the first exemplary embodiment. Also, the configurationenables reduction of dark current intruding into the charge storingportion 3 a. Also, the first isolation portion 14 is provided between aphotoelectric conversion portion 2 a and a photoelectric conversionportion 2 c of the third pixel 13 c. Such configuration enablesreduction of dark current intruding into the photoelectric conversionportion 2 a and the photoelectric conversion portion 2 c. Also, a secondisolation portion 1 is arranged between a transistor and the chargestoring portion 3 a or the photoelectric conversion portion 2 a,enabling suppression of a decrease in pressure resistance and occurrenceof parasitic MOS transistors. A description thereof will be providedwith reference to the schematic cross-sectional view in FIG. 5.

FIG. 5A is a schematic cross-sectional view taken along line 5A-5A inFIG. 4, and FIG. 5B is a schematic cross-sectional view taken along theline 5B-5B in FIG. 4. In FIGS. 5A and 5B, the same components as thosein FIGS. 3A and 3B are provided with the same reference numerals, and afurther description will be omitted. A description of the configurationillustrated in FIG. 5A will be omitted because the configuration isalmost the same as that in FIG. 3A. In FIG. 5B, the charge storingportion 3 a of the first pixel 13 a and the charge storing portion 3 cof the third pixel 13 c are adjacent to each other, and are blocked fromlight by the same light shielding film 20. By means of this lightshielding film 20, no light enters between the charge storing portion 3a and the charge storing portion 3 c. However, the first isolationportion 14, i.e., a second conductivity type semiconductor region 22, isarranged instead of an insulator 23 of the second isolation portion 1,which easily generates dark current. Such configuration enablesreduction of dark current intruding into the charge storing portion 3 aand the charge storing portion 3 c.

As described above, a first isolation portion is arranged between acharge storing portion of a pixel and a charge storing portion of anadjacent pixel, enabling reduction of alias (error signal) due to lightscattering occurring when a second isolation portion is arranged. Also,intrusion of dark current into the charge storing portions can bereduced. Also, similar advantages can be provided to the areas aroundphotoelectric conversion portions by a similar arrangement. In additionto the above, a second isolation portion is provided between the chargestoring portion and a transistor, enabling enhancement of pressureresistance and reduction of occurrence of a parasitic MOS transistor. Itshould be noted that the isolation region arrangement according to thepresent exemplary embodiment can also be applied to a different planlayout.

Third Exemplary Embodiment

For the present exemplary embodiment, a pixel circuit, which isdifferent from that illustrated in FIG. 1, will be described withreference to FIG. 7. FIG. 7 illustrates a configuration including apixel unit 22. The same components as those in FIG. 1 are provided withthe same reference numerals and a description thereof will be omitted.

FIG. 7 illustrates a first photoelectric conversion element 2 a, asecond photoelectric conversion element 2 b, a first charge storageelement 3 a and a second charge storage element 3 b. A first gateelectrode 8 a and a second gate electrode 9 a are provided for the firstphotoelectric conversion element, and a first gate electrode 8 b and asecond gate electrode 9 b are provided for the second photoelectricconversion element. A discharging portion 23 a is provided for the firstphotoelectric conversion element, and a discharging portion 23 b isprovided for the second photoelectric conversion element. The firstphotoelectric conversion element 2 a and the second photoelectricconversion element 2 b share a floating diffusion region 4, a resettransistor, a selection transistor and an amplification transistor.

In other words, the pixel circuit in FIG. 7 has a configuration in whichthe floating diffusion regions 4 of a pixel in the n-th row and the m-thcolumn and a pixel in the n+1-th row and the m-th column in FIG. 1 areconnected to each other. The reset transistor, the selection transistorand the amplification transistor are shared. Also, the configuration inFIG. 1 can be regarded as the case where the pixel unit 22 includes onephotoelectric conversion portion 2.

According to the above-described configuration, the number of elementscan be reduced compared to the configuration in FIG. 1, enabling theareas of the charge storing portions and the photoelectric conversionportions to be increased.

For arrangement of isolation regions in this case, as illustrated in thesecond exemplary embodiment, it is desirable to arrange second isolationportions between the charge storing portions and the transistors, and toarrange first isolation portions in the following areas: first, theareas between area charge storing portions, for example, the areabetween the first charge storage element 3 a and the second chargestorage element 3 b, and the area between the first charge storageelement 3 a and a charge storing portion of an adjacent pixel unit; andfurthermore, the areas between charge storing portions and photoelectricconversion portions, for example, the area between the first chargestorage element 3 a and the second photoelectric conversion element 2 b,and the area between the first charge storage element 3 a and aphotoelectric conversion portion of an adjacent pixel unit. As describedabove, as a result of the first isolation portions and the secondisolation portions being arranged as illustrated in the second exemplaryembodiment, intrusion of charges into the charge storing portions can bereduced while maintaining pressure resistance.

Application to an Imaging System

The present exemplary embodiment will be described in terms of the casewhere a photoelectric conversion apparatus according to the firstexemplary embodiment and the third exemplary embodiment is applied to animaging system, with reference to FIG. 8. An imaging system may be adigital still camera, a digital video camera, or a digital camera for amobile phone.

FIG. 8 is a diagram illustrating the configuration of a digital stillcamera. An optical image of a subject is formed on an imaging plane in aphotoelectric conversion apparatus 804 via an optical system including alens 802. Outside the lens 802, a barrier 801, which provides aprotection function for the lens 802 and also serves as a main switch,may be provided. A diaphragm 803 for adjusting the amount of lightemitted from the lens 802 may be provided to the lens 802. Imagingsignals output from the photoelectric conversion apparatus 804 via aplurality of channels are subjected to processing such as variouscorrections and clamping, by means of an imaging signal processingcircuit 805. Analog-digital conversion of the imaging signals outputfrom the imaging signal processing circuit 805 via the plurality ofchannels is performed by means of an A/D converter 806. The image dataoutput from the A/D converter 806 is subjected to various corrections,data compression, etc., by means of a signal processing unit (imageprocessing unit) 807. The photoelectric conversion apparatus 804, theimaging signal processing circuit 805, the A/D converter 806 and thesignal processing unit 807 operate according to a timing signalgenerated by a timing generator 808. Each block is controlled by a wholecontrolling and arithmetic operation unit 809. The digital still camerafurther includes a memory unit 810 for temporarily storing image data,and a recording medium control I/F unit 811 for recording/reading imagesin/from a recording medium. A recording medium 812 includes, e.g., asemiconductor memory, can be attached/detached. The digital still cameramay further include an external interface (I/F) unit 813 forcommunication with external computers, etc. Here, the imaging signalprocessing circuit 805, the A/D converter 806 and the signal processingunit 807 and the timing generator 808 may be formed on the same chip asone on which the photoelectric conversion apparatus 804 is formed.

Next, operation in FIG. 8 will be described. In response to the barrier801 being opened, main power, power for a control system, and power forimaging system circuits such as the A/D converter 806 are sequentiallyturned on. Subsequently, in order to control the exposure amount, thewhole controlling and arithmetic operation unit 809 makes the diaphragm803 open. Signals output from the photoelectric conversion apparatus 804pass through the imaging signal processing circuit 805 and are providedto the A/D converter 806. The A/D converter 806 performs A/D conversionof the signals and outputs the signals to the signal processing unit807. The signal processing unit 807 processes the data and provides thedata to the whole controlling and arithmetic operation unit 809, and thewhole controlling and arithmetic operation unit 809 performs anarithmetic operation to determine the exposure amount. The wholecontrolling and arithmetic operation unit 809 controls the diaphragmbased on the determined exposure amount.

Next, the whole controlling and arithmetic operation unit 809 extractshigh-frequency components from the signals output from the photoelectricconversion apparatus 804 and then processed by the signal processingunit 807, and performs an arithmetic operation to determine the distanceto the subject based on the high-frequency components. Subsequently, thelens 802 is driven and whether or not the camera is in focus isdetermined. If the camera is determined as not in focus, the lens 802 isdriven and an arithmetic operation to determine the distance isperformed again.

After confirming that the camera is in focus, exposure starts. After theend of the exposure, the imaging signals output from the photoelectricconversion apparatus 804 are subjected to, e.g., correction, in theimaging signal processing circuit 805, subjected to A/D conversion inthe A/D converter 806, and are processed in the signal processing unit807. The image data processed in the signal processing unit 807 areaccumulated in the memory unit 810 by means of the whole controlling andarithmetic operation unit 809. Subsequently, the image data accumulatedin the memory unit 810 is recorded in the recording medium 812 via therecord medium control I/F unit by means of the whole controlling andarithmetic operation unit 809's control. The image data is also providedto, e.g., a computer via the external I/F unit 813 and processed.

As described above, a photoelectric conversion apparatus according tothe present invention is applied to an imaging system. As a result ofusing a photoelectric conversion apparatus according to the presentinvention, noise superimposed on image signals as a result of use of aglobal shutter can be reduced, enabling provision of higher-qualityimages. Also, noise removal in, e.g., a signal processing circuit can befacilitated.

Several exemplary embodiments of the present invention have beendescribed above. However, the present invention will not be limited tothe exemplary embodiments and appropriate modifications are possible.For example, the pixel circuit configuration is not limited theconfiguration in FIG. 1. The configuration may be a configuration inwhich charges are discharged in a vertical direction of thesemiconductor substrate, rather than from the discharging portionillustrated in FIG. 1. Also, the configuration of the first gateelectrode 8 is not limited to those described for the exemplaryembodiments, and the first gate electrode 8 may not extend to the areaabove the charge storing portion 3. The polarities of the charges, thesemiconductor regions and the transistors may appropriately be changed.Also, any appropriate combination of the exemplary embodiments ispossible.

While the present invention has been described with reference toexemplary embodiments, it is to be understood that the invention is notlimited to the disclosed exemplary embodiments.

This application claims the benefit of Japanese Patent Application No.2008-123440, filed May 9, 2008, which is hereby incorporated byreference in its entirety.

1. A photoelectric conversion apparatus comprising a pixel unitincluding: a photoelectric conversion portion including at least a firstphotoelectric conversion element; a charge storing portion including atleast a first charge storage element, and holding the charge generatedin the photoelectric conversion portion; a plurality of transistors foroutputting a signal based on the charge held by the charge storingportion; and an isolation area for electrically isolating the chargestoring portion, wherein the isolation area includes a first isolationportion having a PN junction; and a second isolation portion having aninsulator and arranged between the first charge storage element and atleast a part of the plurality of transistors. 2.-9. (canceled)